Embedded Microstructure Fabrication Using Developer-Permeability of Semi-Cross-Linked Negative Resist

This paper reports on a novel and simple 3-D fabrication technique of microstructures embedded in a single-layer negative resist. The proposed technique allows one the fabrication of an embedded microstructure with a single exposure and the subsequent development process. The unique feature of the proposed fabrication technique is the development method which enables the rapid fabrication of polymer-based microfluidic systems with relatively large areas but with micrometer-sized features. For example, features of microchannels, on the order of 100 m in width and 50 mm in length, sufficient for microfluidic systems, were successfully fabricated with a relatively short (<; 20 min) development time. These features are realized by the interesting physical response of the top-membrane to the developer; the developer permeates through the top-membrane region made of semi-cross-linked photoresist, and the permeated developer dissolves the uncross-linked photoresist at the same time. As a step toward the practical use of the proposed development method, process parameter sets (exposure dose, postexposure bake (PEB) time, and temperature) related to the cross-linking reaction of the top-membrane region were investigated by employing the cross-linking reaction model describing the chemical reaction during the UV exposure and the PEB. Through a series of experiments, 1) a criterion of process parameter sets for the fabrication of centimeter-long embedded microchannels was obtained, and 2) the applicability to polymer-based microfluidic systems was successfully demonstrated.